The present invention is directed to a proportional plus integral, full servo-reversible speed control for a system driving a load in both a forward and reverse direction of travel.
Known closed loop speed controls for systems providing travel in one direction typically include a pulse pickup device for sensing the actual speed of an output shaft to provide feedback information which is used to maintain the actual output speed within a given range of the desired output speed. However, because pulse pickup devices are not sensitive to the direction of travel of the output, they have not been employed in known closed loop speed controls for systems providing travel in both a forward and reverse direction.
An object of the invention is to provide a full servo-reversible speed control for travel in one direction, down through zero speed and up in the opposite direction, the control employing a pulse pickup device for providing feedback information indicative of the actual speed of the output.
A further object of the invention is to provide a proportional plus integral servo-reversible speed control for a system providing motion in both a forward and reverse direction.
The servo-reversible speed control includes a control member which provides a command voltage having a magnitude proportional to the desired output speed for motion in a first direction and having a magnitude inversely proportional to the desired output speed for motion in a second direction. A pulse pick-up device and frequency to voltage converter provide a voltage proportional to the actual output speed, the actual speed voltage being applied to both an inverting and noninverting amplifier. The actual speed voltage is applied as feedback to a proportional plus integral circuit from the noninverting amplifier for sensed motion in the first direction or from the inverting amplifier for sensed motion in the second direction to provide a closed loop speed control for motion in one direction, down through zero speed and up in the opposite direction. The proportional plus integral circuit is responsive to the command voltage and the actual speed voltage gated thereto to maintain the output speed constant.
The speed control includes an acceleration/deceleration limiter which is responsive to the command voltage to provide an essentially linear rate of acceleration or deceleration.
The speed control also includes a saturation gain stage for generating a step voltage output which is combined with the output of the proportional plus integral circuit to overcome the deadband between the threshold of motion in the first and second directions.
For use in a vibratory compactor having front and rear vibrators, the speed control includes an automatic start control which automatically actuates the vibrators in response to the actual speed and direction of travel of the compactor.
Further advantages of the invention will be apparent from the following specification and the drawing.